The present invention relates to devices for the quality control of the electrical insulation of printed circuits made in particular in multiple layers superposed on insulating supports of laminar structure by means of conventional or hybrid technologies.
It is well known in industrial circles specializing in the design and production of complex printed circuits that it is of great importance to reveal their defects in quality as soon as possible in the process of manufacture in order to avoid rejects which are all the more expensive as printed circuits have additional technological value and any flaw, particularly in insulation, proves most often to be irreparable.
With this concern which is essentially an economic one, the present state of the art in the quality control or testing of the functional insulation of multilayer printed circuits consists in employing a system of sensors incorporating elastic conducting tips simultaneously applied on each of the conducting contacts present on the accessible faces of the printed circuit to be tested. Each of these sensors is connected to an insulation indicator via a logic unit of selective--or combinative--interconnection of which the scanning program is specifically established as a function of the typical features of the printed circuit to be tested. The major drawback of this technique lies in the fact that it requires a sensor device with multiple tips whose configuration must be adapted to each particular model of printed circuit.
In fact, this embodiment which is always expensive and whose reliability is often problematic for adaptation to printed circuits of "normal" dimensions, becomes virtually impossible to produce in economically acceptable and technically reliable manner in the majority of industrial applications--particularly in the domain of aeronautical and space equipment--where, for reasons of compactness and circuit density, special printed circuits must be made whose structural characteristics do not correspond to any dimensional standard which would allow the same sensor device, adaptable to several different designs of printed circuits, to be used.
It is therefore an object of the present invention to propose an economical and reliable device for the quality control testing of the insulation of multilayer printed circuits of various types and configurations -- including the most compact and the most complex obtained in hybrid technology--which does not have the drawbacks of the known systems requiring different sets of sensors with tips to be produced and employed.